Quite straightforward. Send the following from your side:
A letter of employment for you and or your wife.
Copy of bank statements for 3 months.
Copies of pay stubs for 3 months.
Copies of your green cards (front and back).
Copy of ALL pages of your/wife's passport.
Notarized affidavit of support form I-134.
A letter addressed to US consulate explaining the nature and duration of intended visit. Include any travel plans inside US.
Your wife's parents need to include:
Filled out visa forms, fees, photos, valid passports.
Proof of source of income and ties to their country.
Sometimes documents establishing relationship is also required. A birth certificate or electoral records showing names of the sponsor and visitor together in one document will help.
In which country will they be applying?